VANCOUVER, B.C. -- Evidence of the teratogenic effects of many older generation anticonvulsants is strong, but data on the newer generation drugs remain inconclusive, Dr. Lewis B. Holmes said at the annual meeting of the Teratology Society.
Anticonvulsants represent one of the most common potential teratogenic drug exposures. Cohort and case studies show that older drugs such as carbamazepine, phenytoin, phenobarbital, and valproate can have effects ranging from major malformations and midface and digit hypoplasia to growth restriction and cognitive dysfunction.
While data on the teratogenic effects of newer anticonvulsants are strong, few research efforts offer an ideal cohort study with a well-assembled comparison group, said Dr. Holmes of Massachusetts General Hospital in Boston.
Small studies that have generated some insight into the new generation of anticonvulsants have focused on lamotrigine (804 pregnancies): clonazepam (70 pregnancies); and gabapentin (48 pregnancies), however, none of the studies has been large enough to offer definitive results, according to Dr. Holmes.
The most promising hope for obtaining enough patients for a sound study lies in pregnancy registries, Dr. Holmes said.
Registries to report anticonvulsant drug use in pregnancy have been developed in North America, Australia, and the United Kingdom, as well as in 37 countries participating in the European Register for Pregnancies with Antiepileptic Drugs.
But work on the studies has so far focused mainly on major malformations, which represent only some of the potential effects of the drugs, explained Dr. Holmes.
Broad inconsistencies in the international registries' methodologies prevent the data from being combined to offer a larger perspective.
"The problem is methodology--there are different definitions of major malformations being used, different time windows for determining the presence of the malformations, and other differences, so sadly a lumping together of findings would not really work," said Dr. Holmes.
Research efforts are also complicated by many women's reluctance to give researchers access to their children's medical records.
"A significant number of women who sign up for registries will balk at signing forms to have records on their child released," he said. "There is a lot of anxiety about the records somehow being used against the child's best interest in the future, so a lot of women will enroll but not give permission to get the records."
"Hopefully, meaningful data will come out on these drugs in a reasonable amount of time," he added. "But it will not be as quick as everyone thinks it's going to be."
ARTICLES BY NANCY A. MELVILLE
Contributing Writer
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